1. Field of the Invention
The present invention relates to an electric motor in which a field magnet is held within a rotor core.
2. Description of the Related Art
An electric motor for motor vehicles such as cars and the like is used in a vibrating environment and therefore is required to exhibit increased reliability. An IPM (Interior Permanent Magnet) motor in which field magnets employed in a rotor unit of the motor are held within a rotor core to prevent radial movement thereof has often been used. In the IPM motor, the radial and circumferential movement of the field magnets is prevented by the rotor core. However, a need exists to additionally provide a means for preventing axial movement of the field magnets.
For example, in a conventional motor manufacturing method, permanent magnets are shrink-fitted into respective holes of a rotor core. Thereafter, end plates are attached to a rotor so that the protrusions formed in the end plates can make contact with the axial end surfaces of the permanent magnets. Then the end plates are fixed to the rotor by fastening means such as caulking pins, bolts and nuts.
Reduced size and increased output power are required in an electric motor for motor vehicles. In a conventional electric motor, however, the axial size of a rotor becomes greater because the end plates are fixed to the opposite end portions of the rotor by bolts or the like.